1. Field of the Invention
The present invention generally relates to a mobile communications system, and in particular to a mobile communications system connected to an integrated services digital network (ISDN) and a call setup method and system from a mobile terminal to the ISDN network.
2. Description of the Related Art
A mobile communications network connected to a fixed communications network has been disclosed in Japanese Patent Unexamined Publication No. 8-70335. A mobile communication switching system of the mobile communications network is provided with a plurality of wireless protocol controllers and a plurality of wired protocol controllers. In the case where a connection is set up between a mobile terminal and a data terminal connected to the fixed communications network, a pair of wireless and wired protocol controllers are selected to allow data communications between the mobile terminal and the data terminal.
Such a data communications system is used to provide a subscriber of the mobile communication system with Group 3 facsimile communication service, V. 42ANNEX modem communication service and high-speed data transmission service. These services are proposed as follows. The Group 3 facsimile communication service uses ARQ (Automatic Repeat Request) procedure for wireless-section protocol and ITU-T Recommendation T.30 and T.4 for wired-section protocol. The V.42ANNEX modem communication service uses FEC (Forward Error Correction) procedure and bit-interleave scheme for wireless-section protocol and ITU-T Recommendation V.42ANNEX for wired-section protocol. The high-speed data transmission service uses ARQ procedure for wireless-section protocol and arbitrary data circuit-terminating equipment (DCE) for wired-section protocol.
When a mobile terminal requests a call setup for data communication, however, some disadvantages are developed. In the case where a new data communication service is provided to the existing mobile communications system, it is necessary to provide all the mobile terminals with a new function of specifying the respective types of wireless and wired data communication protocols and producing a circuit switching signal including them.
Therefore, the user must know the wired data communication protocol used by the data terminal of an opposite party before a mobile terminal requests a call setup for data communication.
Further, the existing mobile communications system is not provided with a means for terminating the wired data communication protocol required to communicate with an ISDN terminal, Therefore, the mobile terminal cannot be connected to the ISDN terminal.